But unrelated outbreaks among Central Africa’s great ape populations could happen at any time, says a report from the International Union for Conservation of Nature (IUCN). The study estimates that Ebola has wiped out thousands of gorillas and chimpanzees since the early 2000s, with some rainforests experiencing a 90 per cent decline in their great ape populations.

The last Ebola outbreak in Central Africa to affect great apes was in 2005. Since then, no further instances of Ebola among great apes have been documented.

But according to Doug Cress, who coordinates the UN’s Great Apes Survival Partnership programme, the situation is “a waiting game”. He fears that, if no vaccine is forthcoming, the next outbreak could wipe out some ape populations already decimated by poaching, disease and habitat loss.

“[Central Africa] is where the largest populations of gorillas and chimpanzees are, but also where the fastest growing human populations are,” he says. “Traditionally, it’s where some of the deadliest diseases have broken out, and there is also political and civic instability. It’s a perfect storm that needs to be addressed.”

The IUCN report, which was written last year but only announced this month, suggests conservation strategies to 2025. It says the rush to create a human vaccine for Ebola sparked by the West African outbreak is an opportunity to develop a vaccine for the central chimpanzee and the critically endangered western lowland gorilla.

But it admits that, even with an effective vaccine, it could prove technically tricky to vaccinate these wild and free-ranging animals.

Survival of the animals is seen as essential for local forest health and economic development. “Great apes are crucial for the forests of the region. They are responsible for seed dispersal and create light gaps in the forests,” says Cress. “They are also beneficial economically for the Rwandan and Ugandan tourism industries.”

The report calls for sustained research funding into the spread and prevalence of Ebola among great apes. This could help predict human outbreaks, says David Pigott, an epidemiologist from the University of Oxford in the United Kingdom, who has studied the conditions that led to Ebola cases in humans before the present epidemic.

Pigott found that in areas where dense vegetation and forests were more prevalent, Ebola outbreaks become more likely.

It is still unclear whether settlements become vulnerable to Ebola because of human encroachment into forest and the resulting deforestation, or whether the disease is passed on by hunting apes carrying the virus, says Pigott. Nonetheless, a vaccine for apes could reduce the risk of Ebola spreading from great ape populations to humans, the report states.